This is a warning, not an error. See diagnostics. You can suppress that warning by disabling the warning:
no warnings 'once';
In reply to Re^4: Supressing error messages on serial port open in Linux
by Corion
in thread Supressing error messages on serial port open in Linux
by pashanoid
| For: | Use: | ||
| & | & | ||
| < | < | ||
| > | > | ||
| [ | [ | ||
| ] | ] |